Fostech’s Echo Sport is designed as a lower-cost alternative to those who want an Echo trigger for their AR, but want to spend a bit less money. Rather than activate the Echo mode from the selector, the Echo Sport features a selector paddle that sits within the trigger well. The shooters moves the paddle to the left for Echo mode, and to the right for semi-auto. And, as with the standard Echo, the Echo mode can be turned off by moving the paddle back to semi-auto mode when the trigger is depressed.
fostech.us/accessories/echo-s-port-triggers/echo-sport-trigger-for-the-ar-15-platform